if your building to the same relative strength, "its six of one , half dozen of another"

the smaller diameter material and lighter wall means youll need more triangulation over shorter spans. ie. the maserati bird cage design of the early 60's. it had 1/2 - 3/4 and 1" running everywhere but it was the lightest most rigid thing out there at the time.

the larger dia material will go longer spans with less triangulation, which equals less joints (work) and less running feet of tube used - but not nessecerily less actual material by weight. IMHO bigger tubes look proportionally correct on a full size - but in the end it all comes down to the actual design and what you want it to do.